Restructuring and repeater mode

I'm currently using a WRT-54GL running Tomato-USB that does all the work. It however tends to run out of RAM with lots of connections open and occasionally crashes. Its predecessor also suffered a hit by lightning.

Since I'm already trying to restructure my network, I want to improve upon it.
All critical networked machines are upstairs. They mustn't lose power or network.
In order to prevent future lightning strikes onto them, they will be put into "island" mode as soon as a thunderstorm's a-brewing. This means severing all physical connections to the outside and switching power to an UPS. But what about networking?

Currently:
The 54GL sits upstairs with a long cable running downstairs to the DSL modem. It is the center of the network, with wired and wireless clients attached to it.
The cable is a possible threat, allowing lightning into the island.

The plan:
I am going to buy an Asus RT-N16, which will be downstairs next to the modem.
My current 54GL will remain upstairs, establishing the bridge to the Asus for all wired devices instead of acting as a router.

This way, in case of lightning, only the Asus and the modem will be sacrificed, the island will be save.

My questions:
- Are there any obvious flaws with this setup? (yes I am aware that speed will be diminished due to the 54GL's slow wireless interface)

- In online games, will the ping suffer much over that wireless bridge? How reliable is such a connection, assuming decent signal strength?

- I want all wireless devices to be able to seamlessly and transparently switch between connecting to the Asus and WRT. As far as I know, that's what "repeaters" do. Tomato offers some Wireless modes, but repeater doesn't seem to be among them. Is it possible to do that, or do I need to buy a new endpoint?